1. Field of the Invention
The present invention relates to a signal processing apparatus and method in a communication system called a multi-input/multi-output (MIMO) system in which transmitting and receiving ends commonly use multiple antennas
2. Description of the Related Art
In the field of the related art, the MIMO mobile communication system is known to achieve more enhanced capability compared to a single antenna system, namely, a single antenna-to-single antenna or a multi-antenna-to-single antenna system.
However, to attain such improvement, an abundant scattering environment should be provided so that signals reaching to multiple reception antennas cannot be correlated. If the correlation among signals is neglected, performance would be degraded and capability would be reduced.
FIGS. 1 and 2 show a related art MIMO communication system employing a PARC (Per-Antenna Rate Control) method.
The PARC refers to a method based on the construction of a V-BLAST (Vertical Bell Laboratories Layered Space Time) system, one of conventional techniques of the MIMO system, in which symbols of signals are differently channel-coded and modulated according to each transmission antenna in a transmitting end with reference to channel information determined at a receiving end and then the corresponding signals are transmitted through each transmission antenna.
FIG. 1 is a view showing the construction of the transmitting end of the related art MIMO communication system employing the PARC method. The operation of the MIMO communication system employing the PARC method will now be described with reference to FIG. 1.
High speed data streams sequentially generated from the transmitting end is demultiplexed through a demultiplexer DEMUX 110 so as to be transmitted from each of multiple transmission antennas. Herein, the demultiplexing means dividing consistent data into a plurality of sub-data according to a determined regulation. FIG. 1 shows two antennas for the sake of explanation.
The demultiplexed sub-streams of each transmission antenna are coded and interleaved in signal processors 121 and 122, and then mapped to a symbol, respectively.
The mapped symbols are inputted to a spreader 131 in which a spreading code1 is multiplied thereto, coded into a scrambling code, and then transmitted to respective transmission antennas 161 and 162.
If a user occupies 10 channels discriminated by the spreading code, the divided sub-streams are divided again into 10 sub-streams, respectively. Respective divided data symbols are inputted into spreaders 131˜133, in which each spreading code 1˜10 is multiplied thereto, added in adders 141 and 142, coded into a scrambling code, and then, transmitted through respective transmission antennas 161 and 162. Herein, generally, one scrambling code is allocated per user. The number of bits allocated to the transmission antennas 161 and 162 can differ depending on a designated data rate.
The coding is made only in a temporal dimension, so its data restoration performance is not as high as that in the space-time coding which is used in a single-rate system. The coding in the temporal domain allows post-decoding interference cancellation, by which performance of a receiver is enhanced.
FIG. 2 is a view showing the construction of a receiving end of the related art MIMO communication system employing the PARC method. The operation of the receiving end of the MIMO communication system employing the PARC method will now be described with reference to FIG. 2.
After the data is demultiplexed and then coded into the scrambling code in the transmitting end, the signals of each transmission antenna can be independently decoded in the receiving end as shown in FIG. 2.
In other words, when the reception antennas 211 and 212 receive the symbol, symbols of each channel are estimated in a symbol detector according to a minimum mean square error (MMSE) method, despread and multiplexed by despreaders 241 and 242 and a multiplexer 250 so that a signal with respect to one antenna can be detected, and the detected signal is relocated (demapped), deinterleaved and then decoded in a signal processor 260.
Thereafter, a signal with respect to the antenna is reconfigured in a signal remover 270 based on the decoded bits and then the reconfigured signal is removed from a reception signal stored in a buffer.
Signals of other antennas are processed in the same manner and along the same path, and then coupled by a coupler 280.
The PARC is a MIMO system technique for a high speed downlink packet access (HSDPA) proposed by Lucent, which allows, unlike the V-BLAST, each transmission antenna to use a different data transmission rate to thereby increase a transmission capacity. In this case, the transmitting end transmits an encoded signal independent by transmission antennas.
The PARC system is different from the V-BLAST system, the existing single-rate MIMO technique in the aspect that each antenna has a different data transmission rate (modulation and coding).
Namely, the PARC system allows each antenna to control the data transmission rate independently more minutely, which leads to enhancement of a substantial transmission capacity of an overall system. In this case, although more bits are required for informing about a state of channels of each antenna than in techniques proposed for the single rate MIMO system, a reference set can be determined.
In other words, in the PARC system, in order to determine a MCS (modulation & Coding Scheme) set valid for each antenna, an SINR (Signal to Interference Noise Ratio) of each transmission antenna as received by each reception antenna is calculated.
At this time, in order to select a channel coding and modulation method to be used at each antenna, the SINR received through each antenna is measured, based on which a combination of a channel coding method and a modulation method to be used at each antenna is selected.
[Table 1] and [Table 2] show examples of combinations of transmission rate of transmitted data and an MCS in the MIMO system having four transmission antennas and four reception antennas.
TABLE 1Data rateCodingbps/Hz(Mbps)Constellationrate37.216 QAM¾24.816 QAM½1.53.6QPSK¾12.4QPSK½0.51.2QPSK¼
TABLE 2Rate:IndexMbpsAnt1Ant2Ant3Ant4128.83333226.43323326.43233426.42333524.02332624.02323724.02233821.62232921.622231019.222221122.821.5331220.421.5231318.021.5221419.221.51.521516.821221625.21.53331722.81.53231822.81.52331920.41.52232018.01.52222119.21.521.522221.61.51.5332321.61.51.5332416.81.51.5222514.41.51.5212615.61.51.51.522715.61.51222824.013332921.613233021.612333119.212233216.812223315.61221.53415.6121.523518.011.5233615.611.5223720.40.52333815.60.52223914.4334014.4334112.0324212.0324312.0234412.023459.622469.622478.421.5488.421.54910.81.535010.81.53518.41.52528.41.52539.613549.613557.23567.23574.82584.82593.61.5603.61.5612.41622.41631.20.5641.20.5
As shown in [Table 1], when the modulation method is performed at 16 QAM and a coding rate is 3/4, the data rate is the maximum, which corresponds the number of transmission bits per unit frequency of 3. And this case can be matched to a case where the SINR calculated at the reception antenna is the maximum.
The next fastest data rate is when the modulation method is performed at the 16 QAM and the coding rate is 1/2, which corresponds the number of transmission bits per unit frequency of 2. In this manner, each number of transmission bits per unit frequency is determined according to the modulation methods and the coding rates, and the number of transmission bits per unit frequency is allocated to the four transmission antennas of [Table 2].
[Table 2] shows examples of combinations of transmission rates in the system using four transmission antennas and four reception antennas. In [Table 2], the index ‘1’ indicates that the number of transmission bits per unit frequency of each of the four transmission antennas is 3 and a data transmission rate is the highest, namely, 28.8.
In such a 4×4 PARC system (namely, the PARC system having four transmission antennas and four reception antennas), in case of the indices from 1 to 38 having a good channel situation because of the relatively shorter distance between the transmitting end and the receiving end, the four transmission antennas can be all used to transmit data, but in case of the indices from 39 to 54 having a bad channel situation because of a relatively longer distance between the transmitting end and the receiving end, two antennas with the larger number of transmission bits per unit frequency are selected from the four transmission antennas to transmit data therethrough.
However, in the afore-mentioned related art, the coding rating and modulation method is separately performed on each antenna in consideration of the channel situation of each antenna, and when the coding is performed, interleaving is also performed, but the interleaving in this context is merely performed in a time domain at each antenna. Thus, the related art fails to perform the interleaving in a space domain with respect to the entire signals to be transmitted through the multiple antennas, so it is disadvantageous in that a space diversity gain cannot be additionally obtained.